Disable sudo, reshuffle travis tasks and introduce caching

Without sudo travis is executing build tasks using docker and waiting
time in this case is really small, usually not longer then 10 seconds.

postgresql-9.5 is installed via addons.apt.packages (without sudo)
But ports 5432 and 5433 are busy. So I had to ajust environment.py to
assign port from higher diapason.

And a few words about build tasks:
First task is used for executing unit tests for all different python versions
The second one is used for executing acceptance tests against etcd
The third one is used for executing acceptance tests against zookeeper
acceptance tests are executed with python2.7 and python3.5

In addition that I've introduced caching of python virtual environment.
It really helps to reduce time needed to install python modules.

features/environment.py

@@ -72,11 +72,13 @@ class AbstractController(object):
 
 
 class PatroniController(AbstractController):
+    __PORT = 5440
     PATRONI_CONFIG = '{}.yml'
     """ starts and stops individual patronis"""
 
     def __init__(self, dcs, name, work_directory, output_dir, tags=None):
         super(PatroniController, self).__init__('patroni_' + name, work_directory, output_dir)
+        PatroniController.__PORT += 1
         self._data_dir = os.path.join(work_directory, 'data', name)
         self._connstring = None
         self._config = self._make_patroni_test_config(name, dcs, tags)
@@ -109,7 +111,11 @@ class PatroniController(AbstractController):
         with open(patroni_config_name) as f:
             config = yaml.load(f)
 
-        self._connstring = self._make_connstring(config)
+        host = config['postgresql']['listen'].split(':')[0]
+
+        config['postgresql']['listen'] = config['postgresql']['connect_address'] = '{0}:{1}'.format(host, self.__PORT)
+
+        self._connstring = 'host={0} port={1} dbname=postgres user=postgres'.format(host, self.__PORT)
 
         config['postgresql'].update({'name': name, 'data_dir': self._data_dir})
         config['postgresql']['parameters'].update({
@@ -133,11 +139,6 @@ class PatroniController(AbstractController):
 
         return patroni_config_path
 
-    @staticmethod
-    def _make_connstring(config):
-        tmp = (config['postgresql']['connect_address'] + ':5432').split(':')
-        return 'host={0} port={1} dbname=postgres user=postgres'.format(*tmp[:2])
-
     def _connection(self):
         if not self._conn or self._conn.closed != 0:
             self._conn = psycopg2.connect(self._connstring)